Where is the pound £ key for voice call multi-factor authentication (MFA) on Microsoft 365 accounts?

The pound key is the hash # key

When a phone number is called during signing into your Microsoft 365 account, voice call multi-factor authentication (MFA), it will ask you to press the pound key which is the hash # key on a standard telephone.

If you're using Webex to answer the call, you may need to press the Keypad button first to show the keypad where to can press the pound / hash # key.

Webex Active Call Window

Webex Multi-Call Window